Overview
Imaging the chemical structure of molecules with atomic resolution was achieved by probing the short-range chemical forces via noncontact atomic force microscopy (NC-AFM). Our low-temperature STM/AFM is based on a qPlus sensor design [1] and is operated in an ultrahigh vacuum at a temperature of 5 K.
The key step to achieving atomic resolution on molecules is the functionalization of the microscope’s tip apex with suitable, atomically well-defined terminations, such as CO molecules (see schematic image). In this case, atomic manipulation techniques are essential for the controlled buildup of the tip used for AFM imaging.
Density functional theory (DFT) calculations are performed to elucidate the physical origin of the observed atomic contrast. The calculations reveal that the Pauli repulsion is the source of the atomic resolution, whereas van der Waals and electrostatic forces only add a diffuse attractive background [2].
